Many integrated circuit (IC) packages use gold wires (“wire bonds”) to transfer electrical signals between an IC die and the leadframe or other packaging substrate on which the die is mounted. With increasing miniaturization of integrated circuits and the corresponding packaging, wire bonds are generally placed closer and closer to each other. When adjacent wire bonds are sufficiently close, transmission of an electrical signal on one wire may cause cross-talk in a neighboring wire, due to a parasitic inductance between the neighboring wire bonds (to which a substrate, or signal paths/traces thereon, may contribute).
FIG. 1 shows an IC die 10 and packaging substrate 20, having wire bonds 12 and 14 therebetween. The parasitic inductance between wire bonds 12 and 14 is shown by the coupled inductor symbol 16 and 18, taken together. A signal transmitted on one of the wire bonds 12 or 14 will induce a small, complementary signal in the other, neighboring wire bond. This small, complementary signal may manifest itself in the form of noise or jitter in the neighboring wire bond.
FIG. 2 shows exemplary terminals on die 10 and substrate 20 for wire bonds 12 and 14. As shown, both wire bonds 12 and 14 are output paths (i.e., they carry output signals from die 10 to substrate 20). A signal originating on die 10 may be output by buffer 32 (in output or I/O block 15) to bond pad 42. Wire bond 12 transfers the signal from bond pad 42 to lead 22 on packaging substrate 20. As shown in FIG. 3, a signal toggling on wire bond 12 (e.g., having a rising or positive transition 30) induces noise having a negative polarity (e.g., in this case, a short falling or negative edge 42 in the waveform 40) on wire bond 14 (e.g., as detected in or around bond area 25). After the transition 30 on wire bond 12 is substantially complete, the negative edge 42 ends, and the level of signal 40 on wire bond 14 returns to its level at t0, prior to transition 30 on wire bond 12. Under some conditions, the induced signal 40 may exhibit a “ringing” characteristic. Such induced signals generally manifest themselves as noise or jitter on neighboring I/O wire bonds.
As operational speeds of I/O signals increase, the need exists to minimize any adverse effects of such induced cross-talk between neighboring I/O signal paths.